help for blood collection and centrifugation for ELISA - (Nov/12/2012 )

Hello!
Is it still okay to centrifuge and collect plasma or serum from frozen rat whole blood samples?
I have frozen rat whole blood samples immediately after collection and stored in -80. I was not able to centrifuge them to collect serum and plasma for ELISA (BDNF or corticosterone) immediately. Is there any protocol for this?
Thanks !!!

-Frankie-

The blood cells will have lysed so you won't be able to efficiently remove them.